Method of making geological explorations



April 16,1935. H; R. PRESCOTT METHOD OF MAKING GEOLOGICAL EXPLORATIONS Fil'ed March 29, 1954 2 Sheets-Sheet 1.

INVENTOR hbm/a'E/ rcscofz ATTORNEY j -April 16, 1935.- H. R. PRESCOTT 1,993,412

METHOD OF MAKING GEOLOGICAL EXPLORATIONS Filed March 29, 1934 2 Sheets-Shet 2 ATTOR I Y Patented Apr. 16, 1935 UNITED STATES.

METHOD OF MAKING GEOLOGICAL I EXPLORATIONS Harold It. Prescott, Ponca City, Okla., assignor to Continental Oil Company, Ponca City, Okla.) corporation of Delaware;

Application March 29.

4 Claims.-

My invention relates to a method of making geological explorations, and more particularly to a method whereby geological explorations are carried out by generating vibrations in the earths 5 surface in such a manner as to eliminate many undesirable vibrations near the origin thereof, and particularly in the vicinity of the earths surface.

ever vibrations pass from one medium into another medium having diiferent' physical characteristics. The reflected or echoed portion of the vibrations travels back to the surface of the earth where suitable seisphones are stationed which are adapted to translate the vibrations into recordable vibrations by electrical or combined electrical and photographic means.

A large part of the vibrations caused by the explosion passes directly to the surface layer of .the earth and causes vibrations of large amplitude near the origin of the' blast for appreciable periods of time. These vibrations are troublesome.

Because of their amplitude they tend to camou- Y flage or mask the reflected or echoed vibrations fromthe various tectonic formations and subsurface strata, In many localities because of the physical character of the surface layers satisfactory exploration of the deep lying geological strata cannot be carried out by means of earth vibrations.

One object of my invention is to provide a method of making geological explorations by means of generating earth vibrations in which trailer waves in the near surfacelayers are minimized.

Another object of my inventionis to provide a method of geological exploration in which the total impact in the near surface layers is reduced While permitting a maximum amount of energy to be delivered tothe deeper geological strata.

Further and other objects of my invention will appear from the following description.

In the accompanying. drawings which form part of the instant specificatiomand which are to be read in conjunction therewith, I

Fig. 1 is a diagrammatic view of a section through the earths surface showing the paths of a number of vibrations at a given instant.

1934, Serial No. 711,932

Figure 2 is a diagrammatic view showing the waves generated by the several charges in Fig. 1 as wouldbe received by a seisphone positioned at pointQinFig. 1.

Fig. 3 is the resultant curve of the sine curves in Fig. 2 showing the resultant of the impulses which would be received by a seisphone at point Q in Fig. 1. a y a Fig. 4 is a diagrammatic view showing wave motions of longer wave lengths than those shownin Fig. 2.

Fig. 5 is the resultant curve of the in Fig. 4.

Fig. 6 is a curve showing the wave motion which would occur if the amount of explosive detonated in accordance with the method of my invention were exploded according to the practice of the prior art.

wave motions In general, my invention provides a method of received if the total amount of explosive were detonated simultaneously. In this manner the reflected or echoed vibrations can be received and recorded. at the surface of the earth by suitable means without the camouflaging or masking effully the equivalent of that which it would have I feet which is-had by the methods of the prior art.

Referring now to the drawings, in the earths surface is'bored a hole 5| having 'a depth D, as indicatedin Fig. 1. Within the hole 5| are placed a number of explosive charges ,I, 2, 3, 4, 5, 6, I, 8, 9 and Ill. The charges may be placed at varying distances from each other. charge distance is equal. The only limitation .with respect to the distances the charges are to be spaced from each other is that no charge shall be at a greater distance from its adjacent charge 9 than that at which the effect of sympathetic deto-,

nation is effective, that is to say, the space between two adjacent charges shall not be greater than the distance at which the detonation of an adjacent, explosive unit will yield suflicient shock to detonate an adjacent unit after the elastic wave given by a unit travels to its adjacent-unit. The reason for this will be apparent from the Usually the intermode of operation, which is as follows. when the uppermost charge I is detonated the vibration wave or explosive impact will travel out from charge I' in all directions. As this impact strikes charge 2, it will cause charge .2 to detonate and the detonation of charge 2 will travel out in all directions. That part of the second impact which travels directly downward will add to the first impact from unit I and the combined resulting impact travels-downwardly to detonate unit 3. The action progresses downwardly from one explosive unit to the next until all of the units are detonated.

By referring to Fig. 1, it will be' observed that there is shown on the figure a plurality of curves l', 2', 3', 4', 5', 6', 'l', 8', 9', and I0. These curves represent the paths of the impacts at a given instant. It is to be remembered, of course that the wave-front travels substantially along the surface of a sphere. Inasmuch as Fig. 1 is a sectional view, the curves I, 2', etc., appear as portions of acircle. It will also be observed that there is a point P at which all of the impacts are united, so that the result is equivalent of a single largeimpact passing downwardly to the geological strata below. At another point, as for example Q, it will also be observed that all of the impacts from the separate explosive units. will arrive at different times. The wave motion at Q from explosive unit I is represented in Fig. 2 by curve l". The wave motion at point Q from explosive unit 2 is represented in Fig. ,2 being curve 2". Similarly the wave motions of respective explosive units 3, 5, 5, 5, l, 8, g and ill at point Q are represented in Fig. 2 by curves 3", 5'1, 5f! 6!! 'lllxsll, s!) and let!- I Fig 3 shows the resulting vibration at point of the separate vibrations given out by the several explosions. It will be observed that the resulting vibration consists of a single impact with no trailer wave motions following, the trailer wave motions having been neutralized by "interference. It will be further obvious by reference to Figs. 2 and 3 that the troublesome trailer vibrations be substantially eliminated by my meth- 0d of' progressive firing forall those frequencies of which the time duration'of one wave length is equal to or less than the time interval for the passing of the impacts from explosive units l to it. For example, if the elapsed time at the point Q from the first impact to the last impact were .1

smooth curve. In Fig. 4 it will be observed that the time elapsing from the first charge to the last charge is less than the wave length of the wave motions. By way of example, I have taken an elapsed timeof firing which is .7 of the time of duration of one wave length. The resultant curve of the wave motions in Fig. 4 appearsdn Fig.5.

It will be observed that the amplitude or of the first impact-is larger than the at of the trailer wave. It will be apparent that though the trailer waves have been reduced in amplitude they have not been fully eliminated. For practical purposes any reduction in the amplitude of the trailer waves is of benefit. It will be also apparent from the foregoing that there is a partial elimination of the trailer waves for all those frequencies of which the time duration of V wave length is equal to or less than the time elapsing from the first impact of the explosive string to the last impact of the explosive string.

By refen'ing to Fig. 6 in which the s me amount of explosive was-used asthat in obtaining the curves in Fig. 4, except detonated simultaneously, it will be observed that'the amplitude Gt of the trailer waves is substantially equal to the amplitude d1 of the first impact. Also it is to be observed that the or of the first impact of Fig. 5 employing the principle of progressive detonation is definitely less than the first impact (11 of Fig. 6 in which simultaneous detonation was used as in the prior art. This is-also very important in reducing undesirable surface vibration.

In the drawings-the showing is theoretical in v that it is assumed the wave fronts will travel in perfect spheres and that the resistance to travel is small. In actual practice the resistance to travel, .of course, naturally reduces the ampli-' trailer waves. This is what I desire inasmuch as I seek to get a maximum impact traveling downwardly.

In the following table Fe represents the fre quency above which elimination of trailer waves is fully effective. Fp represents the frequency above which elimination of trailer waves is par-. tially eflective. The term tp represents the elapsed time of progressive firing from the first to the last ShOt:

ZOllB Fe r 1 .25 2 it. at: 2 $12? if? I 5 (ti/t: 31

In an actual shot in which the depth of the hole was feet and the time i required for the progressive detonation of the explosive units l to It was .025 second, the following table will illustrate the various frequencies showing the limitation of fully effective elimination and partially efiective elimination in the various zones. quencies are given in cycles per second:

CID-Mi Eases Eases Whfle'I have P e out above that I prefer to space the'explosive units at distances no greater than that at which sympathetic detonation may be effected, my method could be used equally well with explosives which would not detonate pro- 'gresslvely, or with the explosive charges placed at greater distances than those at which sympathetic detonation would take place. This could be done by placing electric blasting caps in each unit and connecting the respective lead wires to Fre- 1 I -1,cea,41a a suitable electric tiring device which would space the intervals of detonation according to the needs of the geological locus being explored.-

In actualpractice I have been able to conduct geological explorations in terrains where ordinary methods would have been useless, namely. at Y a point having sand and river fill on the surface.

It will be understood that I have accomplished .the objects of my invention. I am enabled to conduct. geological explorations and eliminate troublesome trailer vibrations at or near the earths surface, and to reduce the amplitude of the primary impacts at or near the earth's surface. In this manner I am able to obtain accurate records which are not camouflaged by troublesome trailer vibrations. By tuning the receiv-' ing instruments to those frequencieswhose trailer waves are eliminated, I am enabled to obtain'an unusually clear record from which satisfactory f results may be obtained It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. Itis further obvious that various changes may be made in details within the scope of my claims without'departing from the spirit of my invention. It is,

therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is: i A

. 1. A method of making geophysical explorations including the step of exploding a substantially vertlcal series of spaced explosive charges in a 2. In a method of making geophysical explcra domain which an explosive is employed-to create. earth vibrations, and reflections of said vibrations are received at or near the earth's surface,

detonating a vertical series of spaced explosive charges in succession from the top downwardly, whereby trailer wave from the detonating charges is reduced inamplitude when received at or near the earth's surface.

3. In the art of creating earth vibrations for geological explorations, detonating a series of vertically spaced explosive charges in succession for a time interval of at least that of the time of duration of one-halfcycle of a wave motion of thedesired frequency, whereby the amplitude of the trailer wave of the impact from the sev eral detonations is reduced when received at or tion of one-half cycle of a wave motion of the desired frequency, whereby the amplitude of the trailer wave of the impact of the resultant of the several detonation's is reduced when receivedat or near the earth's surface.

Kanpur R. Panacea-1'.

tantially vertically position-i 

